The problems encountered in cutting fibers of tow or rope-like feed into staple are well-known in the textile industry. Obtaining staple having a consistent length within a desired tolerance is particularly difficult to achieve. Furthermore, when staple having a greater than desired length is produced, extreme difficulty is encountered by the subsequent processing machinery.
Fusing of the ends of the staple is an additional problem with current cutters since, oftentimes, the cutting force exerted on the tow produces localized heat which may be sufficient to melt the material being processed. Such fusion is especially a problem in the case of tow made of synthetic materials. The heat generated during the cutting of the tow also can cause the production of staple of uneven lengths since the excess heat may cause an undesirable expansion or contraction of the tow during the critical cutting operation. Yet still further, the unwanted heat oftentimes restricts the size and quantity of tow that may be processed by a certain machine.
In certain systems, wetting of the tow or rope is employed to dissipate the undesired heat. This alternative, however, is often unsatisfactory since the required subsequent drying of the tow or rope requires expensive equipment that adds costs to the product. Yet further, the wetting of the tow or rope results in increased handling, packaging and transportation costs.
A number of tow cutters have been proposed for overcoming the above-mentioned difficulties. For example, U.S. Pat. No. 3,768,355 issued to Farmer et al, sets forth an apparatus having a power operated rotatable hollow shaft that has an inlet and an outlet passage for tow or rope. As the tow or rope moves through the passageway, the front end of the tow or rope is forced to impinge against the sharp edges of radially positioned knives to cut the tow or rope into staple of substantially uniform length.
Further, U.S. Pat. No. 3,978,751, which is also issued to Farmer et al., proposes a tow cutting device having a plurality of cam surfaces to accommodate a plurality of tows to enable simultaneous cutting by a single knife assembly. An endless belt is provided between the cam surfaces and the tow, to reduce the frictional engagement between the cam surfaces and the tow thus reducing the heat generating friction to that which would occur between the endless belt and the cam surfaces. Farmer et al. proposes to reduce the heat generated between the belt and the cam surfaces as well by suggesting the use of one of three embodiments. The first embodiment uses an air, gas or liquid bearing medium between the cam surface and the belt; the second embodiment uses a rotating circular cam surface; the third embodiment suggests using both an air, gas or liquid bearing medium and a rotating circular cam surface.
The proposed tow cutting devices, however, do not completely meet the demands of the industry since such machines are oftentimes unduly complicated and expensive. Furthermore, the generation of excessive heat continues to be a problem which both restricts the full capability and reduces the potential efficiency of any particular machine. In particular, the present machines remain unable to produce staple of a desired length within certain low tolerances. The present machines are also restricted to processing tows having a certain range of diameter and quantity.